Joining Small Aluminium Tube

On 5/25/2004 3:10 PM Ted shuffled out of his cave and grunted these great (and sometimes not so great) words of knowledge:
They have specialty rods available for "welding" aluminum. It is actually brazing and done with a propane torch. I have used them in the past on an aluminum storm window frame with excellent results. Your local hardware store should be able to get them for you. If I remember correctly, a pack of 5 rods runs about $10.

Its p[ossible to soft solder it useing aluminium specificflux and a special solder, although for electrical ork, standard multicire seems to work OK,.
However I would regard epoxy as a stringer solution.
I have welded aluminium years ago as an apprentice, usng oxy acetylne. Bloody mess. Very hard to stop it meliting.

If these are to be butt joined, then you will never be able to trust their strength. The brazing rods sometimes work great and other times fail completely. If you are going to slide one inside the other, there are very good structural epoxies for that.
-- Paul McIntosh

What I've actually got is a sort of T-piece, with one length of tube passing at right angles through a hole drilled in the other. After looking a bit deeper on the web, it would appear that I can use silver solder on aluminium, so maybe I'll give that a go.
Thanks for the tips,
Tim

Silver soldering or brazing alloys don't work on aluminum.
See the product selection chart at The fillers of choice for soldering aluminum to aluminum are Alsolder 500 and Al-braze 1070.
Then see the product descriptions at Neither Alsolder 500 nor Al-braze 1070 contain silver.
FWIW.

Well even tho I have been soldering for 40 years (professionally as a TV tech and also as a hobbyist) I have never been able to solder aluminium using standard multicore - in the days when I used aluminium chassis to build radios and amps always had to use a solder lug for the earth connection.
What is your secret?
David
The Natural Philos>

Best results I've had are with a kit of alum rods, stainless wire brush, a 10 inch length of stainless wire about 1/16" diameter and very clear instructions. No flux ! This was marketed by an outfit calling themselves Techno-Weld in UK. The length of wire is referred to as an "abrading tool" ! It worked well every time. Starting with some sample test pieces I eventually graduated to making in-cowl mufflers and repairing broken mufflers which were the trickiest jobs I tried. I have never tried brazing anything required to take heavy, shock loads like a landing gear strut. The trick was always to keep brushing the areas to be joined clean and bright with the brush and difficult corners with the wire abrader. You will need a gas torch of the right size. Small is better - but if too small, the parts won't take - if too large, the parts may melt - especially if the material is thin walled. For in-cowl mufflers, I found it helped to make a "nest" of four bricks around the components - this seemed to help by keeping the heat confined more evenly around the parts - two bricks side by side and two on top making an angle of 90 degrees. Be careful of burning your fingers - I know. Hope this helps.

Not mine. I simply needed to solderalumium tabs on some LIPO cells I had bought. A google search got me to a model train shop who sold me some Carrs Grey Flux. That was the killer breakthrough. With a hotttest irin setting and an open window (fumes are VERY unpleasant), I gobbed this blue jelly onto some baking foil, fed in multicore, and by golly it wetted it!
Once tinned of course the problem was solved.
I note you are in Oz. Try a google search on 'alumiium solder paste' and 'Carrs flux'
Carrs are, I think UK bvased, but have European and commonwealth reach, whereas US suppliers seem to have the paste more.
The paste is, I think, mixture of solder and flux.

Try it, but remember aluminium aircraft are bonded together with epoxy. Given the arrangement you have, that might be the easiest solution, and if you are painting the result, just as acceptable as brazing.

How come no-one has mentioned argon arc welding ? When I was a young sprog (back in the mists of time) aluminium was welded by means of argon arc and (I think - it was a while ago) aluminium rods of different gauge.
The chap who normally did the argon welding was playing about one day and actually welded 2 pieces of aluminium foil together.
Has argon arc gone out with the ark ???
Reg

Seems to me that it's used in some TIG welding:
"Argon is used primarily for its properties an inert gas in applications such as arc welding, steelmaking, heat treating, and electronics manufacturing. It is also widely used as a fill gas in incandescent and fluorescent lamps. In its welding application, straight argon is generally used as a shielding gas in tig welding, while mig welding is usually best suited to a mixture of argon and CO2 as its shielding gas."
"Shielding Gases used in TIG welding:
Argon Argon + Hydrogen Argon/Helium
Helium is generally added to increase heat input (increase welding speed or weld penetration). Hydrogen will result in cleaner looking welds and also increase heat input, however, Hydrogen may promote porosity or hydrogen cracking."
The Tungsten Inert Gas (TIG) welding method was developed in the 1940s for welding of aluminum and magnesium alloys. Besides aluminum and magnesium, the TIG method is used to weld stainless steels, as well as carbon and low-alloy steels. The primary application area for TIG is welding of thin metals, < 6 mm.
In TIG welding, an electric arc is used to heat and melt the material. The electric arc burns between the electrode and the workpiece. A shielding gas that flows through the gas nozzle protects the weld pool and the electrode. The electrode is centrally positioned in the gas nozzle.
The key purpose of the shielding gas in TIG welding is to protect the hot and molten parts of the workpiece, the filler metal and the electrode from the deleterious influence of the surrounding air. In addition, the shielding gas affects the characteristics of the arc and the appearance of the weld.
Typical shielding gases consist of argon, helium or mixtures thereof. The addition of hydrogen or nitrogen can also be beneficial under certain conditions.
Typical applications for TIG welding are welding of pipes, pressure vessels and heat exchangers. Since TIG welding can be used to weld thin metals and small objects, the method is also used in the electronic industry.
The advantages of TIG welding include very high weld quality, absence of slag and very little spatter. The method is extremely versatile, since most weldable materials can be TIG-welded and many welding positions and joint configurations can be used.
Marty

That was mentioned in the original post. Heli-arc welding is the same as the older argon arc welding with only a change in gasses. I don't have the money for the equipment and I doubt that most modelers do, either (judging by how much they complain about a $5.00 increase in dues!)
-- Paul McIntosh

"Heliarc" seems to be a registered trade name for TIG welding:
Advantage Fabricated Metals performs a number of welding processes. The two most common welding processes we use include TIG, an acronym for Tungsten Inert Gas welding and MIG, an acronym for Metal Inert Gas welding. TIG is also referred to as GTAW (Gas Tungsten Arc Welding) and Heliarc®. MIG also is referred to as GMAW (Gas Metal Arc Welding). We also provide oxy-acetylene welding.
TIG welding is also called GTAW (Gas Tungsten Arc Welding) and Heliarc® welding. Heliarc® was the trade name given to the process by Linde's when it was introduced decades ago. The arc is started with a tungsten electrode shielded by inert gas and filler rod is fed into the weld puddle separately. The gas shielding that is required to protect the molten metal from contamination and amperage are supplied during the TIG welding operation.
TIG welding is a slower process than MIG, but it produces a more precise weld and can be used at lower amperages for thinner metal and can even be used on exotic metals. TIG welding is a commonly used high quality welding process. TIG welding has become a popular choice of welding processes when high quality, precision welding is required. The TIG welding process requires more time to learn than MIG. It is similar in technique to gas welding.
Gas tungsten arc welding (GTAW) had its beginnings from an idea by C.L. Coffin to weld in a nonoxidizing gas atmosphere, which he patented in 1890. The concept was further refined in the late 1920s by H.M.Hobart, who used helium for shielding, and P.K. Devers, who used argon. This process was ideal for welding magnesium and also for welding stainless and aluminum. It was perfected in 1941, patented by Meredith, and named Heliarc® welding. It was later licensed to Linde Air Products, where the water-cooled torch was developed. The gas tungsten arc welding process has become one of the most important.
The gas shielded metal arc welding (GMAW) process was successfully developed at Battelle Memorial Institute in 1948 under the sponsorship of the Air Reduction Company. This development utilized the gas shielded arc similar to the gas tungsten arc, but replaced the tungsten electrode with a continuously fed electrode wire. One of the basic changes that made the process more usable was the small-diameter electrode wires and the constant-voltage poser source. This principle had been patented earlier by H.E. Kennedy. The initial introduction of GMAW was for welding nonferrous metals. The high deposition rate led users to try the process on steel. The cost of inert gas was relatively high and the cost savings were not immediately available.
Welding aluminum is done using two preferred methods, both of which employ inert gases, pure argon, or a mix of argon with helium. Any contamination of these gases causes oxidation of the weld, as Uebele inadvertently demonstrated trying to repair a mag-wheel.
?Mag-wheels are not magnesium, you know. They?re aluminum,? Uebele said. ?I knew that, of course, but the weld kept turning black on me. Finally, I checked the gas supply and discovered I was using an argon-carbon dioxide mix. We use carbon dioxide for welding carbon steel. To weld aluminum you?ve got to use pure argon. We don?t use helium here. It?s too expensive. But they do mix argon and helium to increase welding temperatures for thicker sections.? Argon is about ten times the cost of carbon dioxide, commonly used to weld carbon steel. Helium costs another $12 per cubic feet than argon.
...
During WW II, TIG welding was developed. Old timers also called this process heliarc welding. The word heliarc was a trademark of Linde Air Products. Like many known trade marks the name became generic for TIG weld­ing. The Linde Air name was sold to the German subsidiary for $60 million, and Linde became known as Praxair in the U.S.
Today, TIG and MIG welding are the two recommended options for welding aluminum. TIG means tungsten-inert-gas, a shorter acronym for gas-tungsten-­arc-welding (GTAW). The process uses a hand torch with a non-consumable tungsten or tungsten alloy electrode to strike an arc. Pure argon and/or helium, both non-flammable inert gases, provide the shield around the weld to prevent weld contamination from oxides and hydrogen absorption. A filler rod of aluminum is fed into the molten weld, wherever filler is necessary.

go to This stuff works great! It's low temp. so you can use a common torch.
Mike N940AM

What about using JB-Weld?
Steve

Thanks for the informative posts Martin. I remember the argon-arc process from a shipyard back in the early 1960's. There was a welding set (similar to ordinary arc-welder) with the addition of a large argon bottle. The argon was fed by a pipe to the welding tool... this resembled a gun type nozzle. The arc would be started and the gas would surround the area to be welded. Hand held aluninium rods (like in oxy-acetylene welding) were used to feed extra metal into the weld..... it was a long time ago but I remember the setup produced very nice welds and was reputed to be a very bad system to suffer a "flash" from. One guy ended up in hospital his eyes were so badly affected.
I would have thought a small aluminium welding job could be done fairly cheap by most small engineering firms and would be better than messing about with alternatives.
Reg

Just looked at the JB Weld info on the web and may well give this a go. Sounds like a simple alternative.
Thanks,
Tim

You're most welcome. It's a topic that interests me. I'm not a welder; I just play one in my dreams. :o)
That never happens to me in my dreams. All my welds are perfect!
I'm tempted to try my hand at pop rivets & JB Weld. I'd love to be able to cook up totally customized mufflers for myself.
Marty